Database Product Description
- Host Organism
- Solanum lycopersicum (Tomato)
Increased shelf-life (delayed ripening) due to reduced ethylene accumulation through introduction of truncated aminocyclopropane cyclase (ACC) synthase gene.
- Trait Introduction
- Agrobacterium tumefaciens-mediated plant transformation.
- Proposed Use
Production for human consumption.
- Product Developer
- DNA Plant Technology Corporation
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Solanum lycopersicum (Tomato) Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
The tomato is a vine-like herb of the nightshade family (Solanaceae) that also includes potatoes, peppers and eggplants. Botanically this vegetable is a fruit (a berry), which although being a perennial plant in the tropics, is grown as an annual plant in northern climates. The tomato is a native of the Peru, Bolivia, and Ecuador area of the Andes Mountains. Its antiquity is uncertain in regard to cultivation but it was being cultivated when Europeans discovered America. However, it was not generally cultivated in the United States until 1835 because, until then, it was widely believed to be poisonous. Tomatoes are propagated from seeds. In temperate regions seeds are generally started in greenhouses, hotbeds, or cold frames; the plants are set out in the fields when danger of frost is past. Fresh tomatoes are harvested by hand, while those destined for canning or for processing into soups, sauces and ketchups are harvested by machine. The numerous varieties differ greatly in plant form and fruit type, the latter ranging from a small currant size through cherry, plum, and pear forms to the large, nearly round fruits, 10 cm (4 in) or more in diameter, which are the most widely grown. All forms include red- and yellow-fruited varieties. Tomatoes are a valuable source of food minerals and vitamins, and are low in calories. One medium-sized tomato provides 57% of the recommended daily allotment (RDA) of vitamin C, 25% RDA vitamin A, and 8% RDA iron, yet it has only 35 calories. Tomatoes are also rich in an anti-oxidant called lycopene, a carotenoid that has been found to protect cells from oxidants that have been linked to cancer. In laboratory tests, lycopene was found to be twice as powerful as beta-carotene in neutralizing free radicals. Lycopene has been linked to risk reduction for a number of types of cancers, including prostate, lung and stomach, pancreatic, cervical, colorectal, oral and esophageal cancers. In the fresh market industry the tomato fruit is often picked at the mature green or breaker stages for long-distance shipping, and is then subsequently ripened by treatment with the gas, ethylene (12 to 18 h at 20ºC). For processing tomatoes the ethylene-producing compound, ethephon or Ethrel, is applied prior to harvest when only 10% of the fruit is ripe; this accelerates and concentrates fruit ripening and facilitates once-over machine harvest. Tomato line 1345-4 was developed using recombinant DNA techniques to express the trait of delayed ripening of tomato fruit. The transgenic line contains a truncated version of the tomato 1-aminocyclopropane-1-carboxyllic acid (ACC) synthase gene, normally found in tomato. This endogenous enzyme is responsible for the conversion of s-adenosylmethionine to ACC, which is the immediate precursor of ethylene, a phytohormone known to play a key role in fruit ripening. The presence of the truncated ACC synthase gene suppresses the normal expression of the native ACC synthase gene, and while not completely understood, the mechanism of “downregulation” is likely linked to the coordinate suppression of transcription of both the endogenous gene and the introduced truncated ACC synthase gene. The in situ accumulation of ethylene in the transgenic tomatoes was only about 1/50 the level found in the unmodified parental line and the fruit does not fully ripen unless an external source of ethylene is applied. Tomato line 1345-4 was field tested in the United States from 1992 to 1994. The agronomic characteristics of line 1345-4 were evaluated extensively in laboratory, greenhouse, and field experiments. Line 1345-4 retained the agronomic characteristics of the parental tomato, and field reports on seed germination rates, yield characteristics, disease and pest susceptibilities, and fruit compositional analyses determined that this line was comparable to the unmodified parental line, with the exception of reduced ACC synthase activity. Field trial reports demonstrated that transgenic tomato line 1345-4 did not exhibit weedy characteristics, and had no effect on non-target organisms or the general environment. The transformed tomato line was not expected to impact on threatened or endangered species. Cultivated tomatoes are self-fertile, and almost exclusively self-pollinating. Their unique flower and anther morphology makes tomato an essentially cleistogamous plant, in which self-pollination and fertilization occur within an unopened flower. A low crossing rate between tomato varieties was demonstrated and attributed to the limited availability of pollen and poor foraging activity of insect pollinators. Several related species are found as weeds in tomato fields, however, commercial tomato is generally sexually incompatible with these weedy relatives. Two Solanum species, S. lycopersicoides and S. rickii, neither of which is a weed pest in the United States, can be crossed with commercial tomato only under specific, controlled conditions requiring human intervention. The cherry tomato, L. esculentum var. cerasiforme can be crossed with tomato, L. esculentum var. esculentum. However, it would be very unlikely for tomato line 1345-4 to hybridize with cherry tomatoes in the United States since the rate of outcrossing in tomatoes is low and cherry tomatoes are not common in areas devoted to the large-scale cultivation of tomatoes. It was concluded that the chance of genetic exchange among tomato crops was small and outcrossing to other species, even more remote. In the event that an outcrossing event involving pollen from the transgenic tomato line 1345-4 did occur, it was unlikely that the delayed-ripening trait would increase the plant’s weediness or probability of survival. Tomatoes are consumed in both fresh (whole and sliced or diced in a variety of foods) and processed (soups, ketchup, paste, prepared sauces) forms, and the genetic modification introduced into the transgenic tomato line was not expected to result in any changes in consumption patterns. The analysis of nutrients from the novel 1345-4 line and the non-transgenic parental line did not reveal any significant differences in the levels of macro- and micronutrients. Levels of glycoalkaloids present in mature tomatoes from the transgenic line 1345-4 were within the range reported for conventional tomato varieties. The reduced synthesis of native ACC synthase was judged not to have any potential for additional human toxicity or allergenicity. The truncated ACC synthase gene was not expressed in line 1345-4 and should not have any toxic or allergenic properties.
Links to Further Information Expand
This record was last modified on Tuesday, September 15, 2015